1. Field of the Invention
The present invention relates to an apparatus and method for controlling the writing power of an optical disc and more particularly to an apparatus and method for controlling the writing power of an optical disc that takes into consideration a material characteristic deviation between the inner and outer peripheral portions of the optical disc, so as to write data on the optical disc in an optimal state.
2. Description of the Related Art
FIG. 1 illustrates a configuration of a related art optical disc recording/reproducing apparatus. As shown in FIG. 1, the related art recording/reproducing apparatus includes a digital write signal processor 30a which adds an error correction code (ECC) to input digital data, thereby converting the input digital data to have a desired writing format. A channel bit (CB) encoder 40 re-converts the data, previously converted by the digital write signal processor 30a to have the desired writing format, into a write signal in the form of a bit stream. An optic drive 41 outputs a drive signal with a light amount controlled in accordance with a control signal applied thereto. An optical pickup 20 writes the bit stream on an optical disc 10 in accordance with the drive signal, and detects a signal written on the optical disc 10 in the form of a radio frequency (RF) signal. The optical disc 10 may be a recordable compact disc (CD-R), for example.
The recording/reproducing apparatus also includes an RF processor 50 which filters and shapes the RF signal detected by the optical pickup 20 to output a binary signal. A first level detector, indicated as “Level Detector 1,” 51 detects the level (B-level) of a signal reflected from a mark area on the optical disc 10 in a writing operation. A second level detector 52, indicated as “Level Detector 2”, detects the level (RF-level) of the RF signal outputted from the R/F processor 50. A wobble signal detector 53 detects a wobble signal from the reflection signal outputted from the optical pickup 20. An absolute time in pre-groove (ATIP) decoder 54 decodes the wobble signal at the point in time when a particular reproduction pulse duration (for example, 5T) is detected, thereby detecting ATIP data.
The recording/reproducing apparatus further includes a drive unit 60 for driving the optical pickup 20 and a spindle motor 11. A servo unit controls the drive unit 60 in accordance with servo signals. The servo signals include a focusing error (FE) signal and a tracking error (TE) signal. A digital reproduction signal processor 30b recovers the binary signal using a clock phase-synchronized with the binary signal. A microcomputer 70 controls a recording/reproducing operation for the optical disc 10, and also controls the level of writing power in the writing operation.
The microcomputer 70 includes an internal ROM 71 stored with information about optimal write strategies corresponding to respective disc codes for various disc types.
FIGS. 2a and 2b are flow charts illustrating a related art data recording method carried out in the general optical disc recording/reproducing apparatus of FIG. 1. The recording method of FIGS. 2a and 2b is described hereinafter with reference to the configuration of FIG. 1.
When the optical disc 10 is loaded into the recording/reproducing apparatus and subsequently rotated, the optical pickup 20 detects a reflection signal generated as a main beam which is reflected from the optical disc 10. The optical pickup 20 outputs the detected reflection signal to the wobble signal detector 53. The wobble signal detector 53, in turn, detects a wobble signal from the reflection signal. On the other hand, the ATIP decoder 54 samples and decodes the wobble signal at the point in time when a particular reproduction pulse duration is detected, thereby detecting ATIP data. Even when the wobble signal corresponding to a short reproduction pulse duration is sampled, ATIP data can be detected because the ATIP data is low-frequency-modulated data.
The microcomputer 70 detects a disc code from the detected ATIP data, and identifies, in the internal ROM 71, an optimal write strategy corresponding to the detected disc code in step S1 of FIG. 2a. 
If a writing operation is subsequently requested in step S2, the microcomputer 70 performs an optimal power calibration (OPC) operation which detects an optimal writing power at a test area on the inner peripheral portion of the optical disc 10 in step S3. The microcomputer 70 stores the detected optimal writing power and an optimal reflection signal level (B-level) corresponding to the detected optimal writing power.
Thereafter, the microcomputer 70 performs a writing operation at a data area on the optical disc 10 by applying the detected optimal writing power and the identified optimal write strategy in step S4. In the writing operation, the first level detector 51 detects the level of a signal caused by reflection of a write beam, that is, the level of a reflection signal, or the B-level, reflected from the mark area. The second level detector 52 detects the level of an RF signal output from the RF processor 50. At this time, the first level detector 51 detects the B-level of the reflection signal at the point in time when a variation in characteristics of the optical disc medium caused by the write beam is stabilized, for example, at a reproduction pulse duration of 11 T.
The microcomputer 70 determines whether or not a running OPC (ROPC) operation is to be carried out, based on the detected B-level and RF signal level in step S5. If it is determined that it is unnecessary to carry out the ROPC operation in step S6, the microcomputer 70 performs a writing operation while maintaining the optimal writing power detected in accordance with the OPC operation, without performing any ROPC operation in steps S7 and S8.
FIG. 3 depicts a variation in writing power depending on a material characteristic deviation between the inner and outer peripheral portions of an optical disc. Where the optical disc 10 has little material characteristic deviation between its inner and outer peripheral portions, which is indicated as “A” in FIG. 3, it is possible to obtain a desired RF signal level and a desired jitter quality at both the inner and outer peripheral portions of the optical disc 10 even when writing of data is carried out under a condition in which the detected optimal writing power is maintained, without execution of any ROPC operation.
If it is determined in step S5 that it is necessary to carry out an ROPC operation, the microcomputer 70 performs the ROPC. operation until the writing operation is completed in steps S9 and S12. If writing of data is carried out under a condition in which the detected optimal writing power is maintained, and where the optical disc 10 has a substantial material characteristic deviation between its inner and outer peripheral portions, which is indicated as “B” or “B′” in FIG. 3, it is impossible to obtain a desired RF signal level and a desired jitter quality. Thus, a degradation in reproduction characteristics occurs. In order to avoid such a problem, therefore, the microcomputer 70 performs the ROPC operation, based on the detected levels.
The ROPC operation is adapted to continuously adjust the writing power, based on the B-level at the point in time when a variation in characteristics of the optical disc medium caused by the write beam in a writing operation is stabilized, such that the writing power is equal to the detected and stored level of the reflection signal generated at the test area. Since the ROPC operation is effective within an allowable range set with reference to the optimal writing power, it is possible to provide a reproduction signal with a stable level even for an optical disc having a substantial material characteristic deviation between its inner and outer peripheral portions.
However, where an optical disc operating in a low speed mode (for example, at 4X, where ‘X’ denotes a basic reference speed) performs a writing operation in a higher speed mode (for example, at 32X), its writing power is outside of an ROPC margin range from a point substantially corresponding to a point P of FIG. 3 during the ROPC operation, under a condition in which the optical disc has a large material characteristic deviation between its inner and outer peripheral portions (indicated as “C” or “C′” in FIG. 3) in step S10. In this case, write failure may occur because there may no longer be any signal discrimination ability in step S11. Even when there is no write failure, it is impossible to reproduce written signals.